This happened when I was probably six or seven. My parents are divorced, and at the time, I was at my dad's house. We were all out back, and my dad was working on something. He had put a spare screwdriver on the ground, and my eight or nine-year-old sister had picked it up.
She motioned me over to a lounge chair with towels hanging off of it. She told me to crawl under and I did. She told me that we were going to be getting tatoos, and I was to go first. I said okay, and laid down on the ground. She pulled my pants and underwear off, revealing my penis. She touched it, and it grew hard. She started to look at it, and moved it around. I asked her about my tatoo.
'What do you want, because this is going on your thing.' she said.
'Just put Amy.' I said, naming the person I liked at the time. She moved the screwdriver like she was writing, and finished.
'Do you want me to give you one?' I asked innocently. She nodded and we traded places. I asked where she wanted it, and she pulled her pants and panties down revealing her hairless vagina. She spread her legs and stuck her finger in her vagina, spreading the lips apart.
'In there.' She said. 'Just put Brian.' So I stuck the screwdriver, along with my fingers into her slit, not knowing any better. She let out a small moan, and wanted to do me again. We switched places again, and I pulled off my clothes. My penis was still hard, and she started to rub it. I asked her to keep rubbing it because it felt good, and she did. We continued to do this until we were told to go inside. No further experiences.